User terminals capable of cellular communication and wireless local area network (WLAN) communication have become widely used recently. Access points for the WLAN that are managed by operators of the cellular communication network are also increasing. The 3rd Generation Partnership Project (3GPP) has therefore started to study technologies to strengthen interworking between WLAN and cellular radio access network (RAN) (see Non Patent Literature 1).
Meanwhile, a dual connectivity architecture in which a master eNodeB (MeNB) that is a cellular base station for processing data of plural bearers transfers data of some bearers via another cellular base station called a secondary eNodeB (SeNB) to communicate with user terminals has been studied (see Non Patent Literature 2).